If you were to ask the average American to list what the cause of the next global conflict would be, they’d likely list the threats posed by terrorism or rogue regimes brandishing nuclear weapons. What they almost certainly wouldn’t mention is water.

According to a United Nations report presented at U.N. headquarters in New York last week, about 2.9 billion people in 48 countries will be facing water shortages within 10 years that could destabilize and jeopardize the “very existence” of some countries. By 2030, there will be a global supply shortfall of 40%. And it could pose a major threat to global security.

“People do not have the luxury of living without water and when faced with a life or death decision, people tend to do whatever they must to survive,” the report said. “In this manner, changes in fundamental hydrology are likely to cause new kinds of conflict, and it can be expected that both water scarcity and flooding will become major transboundary water issues.”

Global warming is causing extreme weather events that are nudging water supply issues from bad to desperate. On their own, vanishing rivers or droughts could devastate a year’s worth of crops but combined and over time, they pose a civilizational threat. At this point, U.S. intelligence agencies consider the prospect of water shortage a threat to be considered alongside terrorism and weapons of mass destruction.

Understanding the water shortage: To be clear, the world isn’t exactly running out of usable water. Freshwater is a very small portion of the planet’s entire water supply: It accounts for only about 2.5% of all water, and just 1% of freshwater is readily accessible. But it is all over the world, and it’s renewable.

The main problem with water isn’t about total volume — it’s about distribution. Water isn’t always where people need it when they need it, and all societies need it for everything: health, sanitation, agricultural production, energy and industry.

The ability to handle distribution to meet these demands is largely a function of wealth. While affluent countries are generally able to manage the resources to meet demand, poorer countries frequently lack the infrastructure to deliver clean, safe water. Their economies also tend to rely disproportionately on deregulated and dirty extractive industries like coal mining that contaminate already-scarce water supplies.

Impoverished nations are already suffering from serious water woes. Three-quarters of a billion people lack access to clean water, and water-related disease takes the lives of about 840,000 a year, according to Water.org. Women and children spend 140 million hours a day collecting usable water, often from unclean sources.

A growing problem: As the world’s population grows and endures increasingly volatile weather patterns, water management problems are on the brink of becoming far worse for much larger swathes of the global population.

“The ways we need water and the way the environment provides water are increasingly not matching up, because things like climate change make it less and less predictable,” Janet Redman, the climate policy director at the Institute for Policy Studies in Washington D.C., told Mic. “We built our society around when we can get water, when we can grow food, how we have to house ourselves, because we understand the environment around us after living in it for hundreds and hundreds and hundreds of generations.

“The problem now, partly due to climate change, we can’t predict the patterns, of rainfall, where water is going to be when, when things melt, how floods and droughts work — we’re out of sync with the environment because we’ve changed the environment in a pretty significant way.”

How shortages breed conflict: The decline in our ability to predict the flow of the world’s water based on historical patterns, called “relative hydrological stationarity” in the scientific community, is a game changer.

“The loss of stationarity is playing poker with a deck in which new cards you have never seen before keep appearing more and more often, ultimately disrupting your hand to such an extent that the game no longer has coherence or meaning,” the report said.

That trickling in of new cards is dangerous. Lack of water has played a role in countless conflicts on a sub-national level. The Pacific Institute has documented hundreds of instances of water-related conflict in the past half-century which range from Kenyan tribes clashing over water amidst droughts to riots in South Africa over lack of access to clean water.

As water supply experts Shira Yoffe and Aaron Wolf have noted, scarcity of clean freshwater has contributed to many episodes of acute violence on a small geographic scale across the world, such as bloody conflict between states within India over access to the Kaveri River. Adel Darwish, co-author of Water Wars: Coming Conflicts in the Middle East,has argued that access to water has played a significant role in the Arab-Israeli conflict, including the 1967 war.

More recent conflicts include a hidden element of water scarcity to them. Inter-ethnic conflict in in Sudan in the 2000s was also driven by warring over access to clean water. Today, the militant Islamist State group is reportedly using control of water in Iraq and Syria as a tool of war.

It affects everyone: It’s increasingly clear that even rich countries cannot keep their water supplies safe from the consequences of climate change and extreme weather events — or from the instability that follows. In recent years California has experienced its worst drought in recorded history, which has rippled through both the local and national economy. Floods in the Canadian province of Manitoba in 2011 and 2014 caused the government’s budget deficit to swell and ultimately led to political leaders resigning, according to the U.N. report. Insecurity can bubble up in even the places that are taken for granted as stable.

The world’s water supply crisis is a serious one: By 2050, sustaining the planet will require at least 50% morewater than it does today, according to the New Yorker.

But it isn’t hopeless. The global community can develop institutions and technologies designed to enhance water management capabilities and minimize future weather volatility. Many of the policy solutions already exist, and areas prone to conflict can be monitored more closely. What’s most badly needed is political will and action.

This article is published in collaboration with MIT News. Publication does not imply endorsement of views by the World Economic Forum.